This application claims the priority of British Patent Application No. 0007924.4 filed Mar. 31, 2000, the disclosure of which is hereby fully incorporated by reference herein.
The present invention relates to an inverter and more particularly, to an inverter that is able to withstand relatively high voltages.
The invention concerns the problem of fabricating an inverter for use with applied voltages exceeding the magnitude tolerable by the switching devices used in the inverter.
A switching device in a typical half bridge inverter may be subjected to a large portion or possibly all of the voltage applied to the inverter. In a full bridge inverter, each switching device will normally have a maximum of only half the supply voltage connected across it. However, if one switching device is turned on fractionally before its counterpart in the other half of the circuit, its counterpart will be subjected to at least a substantial proportion of the supply voltage. If the voltage rating of the switching device is thereby exceeded, it is likely to fail.
The present invention provides a more reliable inverter circuit that is tolerant of variations in switching speeds of its components. The inverter circuit of the present invention does not permit voltages applied to the switching devices to exceed their rated voltage. Thus, the inverter circuit of the present invention is especially useful for higher voltage applications.
According to the principles of the present invention and in accordance with the described embodiments, the invention provides an inverter circuit for applying a voltage to a load. The inverter circuit has first and second input terminals adapted to be connected to the voltage. First and second switching devices are connected in series at a first junction. The first switching device is connected to the first input terminal, and the second switching device is connected to one side of the load. Third and fourth switching devices are connected in series at a second junction. The third switching device is connected to an opposite side of the load, and the fourth switching device connected to the second input terminal. A voltage divider is connected between the input terminals and provides an output potential. A first current steering device is connected between the output potential from the voltage divider and the first junction. A second current steering device is connected between the output potential from the voltage divider and the second junction. By switching on the second and third switching devices and thereafter the first and fourth switching devices, and then, switching off the first and fourth switching devices before switching off the second and third switching devices, the inverter circuit prevents more than half of the voltage from being connected across any one of the switching devices.
In one aspect of the invention, the inverter circuit further comprises fifth and sixth switching devices connected in series at a third junction. The fifth switching device is connected to the first input terminal, and the sixth switching device is connected to the opposite side of the load. Seventh and eighth switching devices are connected in series at a fourth junction. The seventh switching device is connected to the one side of the load, and the eighth switching device is connected to the second input terminal. A third current steering device is connected between the output potential from the voltage divider and the first junction, and a fourth current steering device is connected between the output potential from the voltage divider and the second junction. By switching on the sixth and seventh switching devices and thereafter the fifth and eighth switching devices, and then, switching off the fifth and eighth switching devices before switching off the sixth and seventh switching devices, the inverter circuit prevents more than half of the voltage from being connected across any one of the switching devices; and further, it applies a voltage across the load in the opposite direction to the first to fourth switching devices.
In another embodiment, the invention further provides a method of operating the inverter circuit described above by first, switching on the second and third switching devices, and thereafter, switching on the first and fourth switching devices. The inverter circuit further operates by switching off the first and fourth switching devices and thereafter, switching off the second and third switching devices to prevent more than half the circuit input voltage being connected across any one of the switching devices.
In one aspect of this embodiment, the inverter circuit operates by switching on the sixth and seventh switching devices and thereafter, switching on the fifth and eighth switching devices. The inverter circuit further operates by switching off the fifth and eighth switching devices and thereafter, switching off the sixth and seventh switching devices. That operation of the inverter circuit prevents more than half the circuit input voltage from being connected across any one of switching devices; and further, it applies a voltage across the load in the opposite direction to the first to fourth switching devices.
These and other objects and advantages of the present invention will become more readily apparent during the following detailed description.